In a modern managed information environment, large volumes of information are stored and processed. Storage takes the form of databases, or specialized mass storage mechanisms adapted for efficient storage and retrieval of the sometimes vast amounts of information stored in the database by an enterprise, organization, or application. In various contexts, certain databases will be replications of all or portions of another database which needs, for various reasons, to store data in an alternate database. Typically, the secondary (standby, replicated, secondary, etc.) database receives logs of changes made to the primary or main database. Such logs are often at a physical storage level, and enumerate changes according to the physical block, segment, track or other structure to which the change was made. However, the secondary database may not share a common physical structure with the primary database to which the logs pertain. Accordingly, the secondary database maintains a data dictionary corresponding to the structure of the data on the primary database. The data dictionary is employed to map logical data changes (changes in terms of database objects, such as SQL tables) to the physical structure, or storage locations, of the data. In this manner, the physical references in the logs may be “reverse mapped” to their logical counterparts so that corresponding changes may be made to the secondary database.
For example,in a modern information processing environment, data repositories, or databases, are often maintained in a redundant manner which minimizes or eliminates data loss in the event of failure. Such a redundant architecture often takes the form of a standby (standby DB) site, or hotsite, which mimics the primary site and receives all database updates so as to maintain a duplicate version of the data stored at the primary site (primary DB). Such a hotsite is typically remote from the primary site to enable the hotsite to commence operation in lieu of the primary site in the event of catastrophic or unexpected failure of the primary site, a so called “failover” operation. The hotsite, or standby site, is therefore enabled to assume operation as the primary site in a seamless manner since the primary and standby databases are maintained in a realtime or near realtime manner, being subject only to transmission latency and processing load delays.
Conventional modern data repositories take the form of a database which provides a normalized arrangement to the data for access via a database management system (DBMS). Often, modern databases take the form of a relational database using a relational DBMS, such as those available commercially form Oracle® corporation of Redwood Shores, Calif., assignee of the present application. A relational database stores data in a set of tables, each having columns of attributes arranged in rows. An often complex network of relationships exists between the database tables. The conventional network of relationships defines an entity-relation diagram (ER diagram), which defines each of the tables and relations to other tables in the relational database. A conventional DBMS is operable to traverse the tables in response to a query to access and/or modify the requested data.
In such a conventional relational database, the tables enumerated by the ER diagram depict a logical organization to the database based on the table and field identity. The table and field identity is independent of a physical arrangement of the actual data on the storage device (e.g. disk drive). Accordingly, in a standby hotsite arrangement, in contrast to a redundanct hardware implementation, similar table and field references are not bound to similar locations on the respective storage device. Therefore, a conventional standby site may support a similar table arrangement at the primary site using a different physical array of storage devices. In this manner, the standby site need not procure an identical hardware arrangement as the primary site, a likely expensive proposition in large data repositories. Further, the standby site may also be operable to perform other storage operations, such as alternate standby support operations for other primary sites, since only the logical table arrangement, and not the physical disk arrangement, needs to be duplicated.